Footwear Comprising an Elastic Intermediate Sole

ABSTRACT

The invention relates to footwear comprising a multi-layer structure of the sole, with said sole being composed of at least one outsole ( 3 ), an optional insole as well as a midsole ( 2 ), wherein the midsole ( 2 ) is made of an elastic material having an open-cell structure provided with a gas- and liquid-tight outer skin, with said cell structure being filled with at least one fluidic medium.

The invention relates to footwear comprising a sole of at least two-layer structure, with said sole consisting of a harder outer sole (outsole), an optional softer inner sole (insole) as well as an elastic intermediate sole (midsole).

During running, the musculoskeletal system is exposed to and must withstand rather significant loads. In the course of time many runners, even those not engaged in competitive sports activities, are prone to suffer from knee and joint trouble that may cause severe problems not only during sports but also as everyday actions and exercises are concerned. With a view to counteracting the loads described hereinbefore cushioning elements have therefore been developed for footwear.

For running shoes quite a number of cushioning concepts have been developed.

The Nike company, for example, developed a system that was based on an air sole. For this purpose, a gas-filled air cushion was integrated into the sole or in portions of the sole of a running shoe. Under load the gas is compressed so that the desired cushioning or damping effect is achieved.

Produced by the company of Adidas a running shoe was known into which compartments filled with air were integrated, said compartments being connected by means of thin flow passages. During running and depending on the loads exerted on the shoe, the air is displaced via the flow passages. In this way as well, a damping effect is brought about.

Put on the market by Reebok was a sole that was provided with an air-filled honeycomb system of polyurethane. The honeycombs were of different size and thus could provide support to certain parts of the foot as individually required. A similar system was developed by the company of Puma.

All these systems suffer from a drawback in that they have been designed to have springlike characteristics. For example, cushioning at the heel results in the pressure to be directly lowered at the beginning of the stance phase of the gait only at the impact point of the heel. At that point, kinetic energy is transformed into static energy which will be stored in the compressed gas the sole contains. As the gait motion continues, power is transmitted over the entire foot and the heel is lifted off progressively. As soon as the heel takes the load off the compressed sole it at the same time returns the stored static energy into the system of the foot in the form of kinetic energy. This gives rise to an additional momentum acting on the ankle joint.

Although, as a result of these additional forces led into the ankle joint, the running process is assisted in a not undesirable manner—as energy being recovered in this way—the underlying target of going easy on and thus protecting the articulation and musculoskeletal system of the runner is nonetheless completely counteracted. In actual fact, additional stresses of considerable magnitude are produced due to this. It is to be remembered in this context that all damping measures of this kind are in point of fact intended to reduce the load acting on the musculoskeletal system.

To make the problem clearer it is to be noted that the maximum heel load arising with a single-leg jump may amount to 3.5 times the body weight. Even during normal gait a load of up to 130% of the body weight acts on the heel.

It is thus the objective of the present invention to provide footwear that during running/walking processes effectively absorbs and eliminates energy acting on the foot and in particular the heel and forefoot.

Said objective is achieved by providing footwear of the kind first mentioned above comprising a midsole made of an elastic material having an open-cell structure provided with a gas- and liquid-tight outer skin, wherein the cell structure is filled with at least one fluidic medium.

Footwear proposed by the present invention may be of optional type, for example may be a running shoe, a shoe intended for everyday use and may also include sandals as well as casual-wear sandals available on the market and known under the term flip-flops. The inventive effect of damping the walking/running movement is reached with all the footwear designed in the inventive manner. A corresponding damping effect may as well be reached with a sockliner.

Footwear proposed by the invention comprises a multi-layer and particularly three-layer sole structure. As a rule, said structure consists of an outsole, an insole as well as a midsole. Moreover, more than only a single midsole may be arranged for, but one of the midsoles must in any case be designed as called for by the present invention. In addition, several insoles may be provided, for example of a kind that exclusively covers either the ball or the heel area. If thought expedient, the outer skin of the midsole may also serve as insole or the insole may be integrated into the midsole.

The midsole is designed so as to be elastic, and thus brings about the innovative damping effect.

For this purpose, the midsole consists of an elastic material having an open-cell structure. The cell structure is filled with a fluidic medium and enclosed by a gas- and liquid-tight outer skin. The open-cell structure of the elastic material allows for the medium to be displaced within the midsole and in this way intercepts part of the load, especially at the heel.

In particular, the elastic material has a spongelike structure as can be achieved, for example, with foamed plastic. Suitable foamed plastic materials are foams known from plastics engineering such as, for example, polyethylene, polypropylene, polystyrene, PET, and polyurethane.

Especially preferred are midsoles made of integrally foamed polyurethane, said midsoles thus having, by default, a closed outer skin and a cellular core. Another and especially well suited material is polyester urethane rubber which offers excellent elastic properties.

It is preferred for the midsole to be manufactured of a material produced by an integral skin foam process in such a manner that outer skin and cellular structure consist of a uniform material. However, another possibility is to provide an open-cell foam body with a skin consisting of a different type of material.

For example, materials may be used that have a weight per unit volume ranging between 40 and 100 kg/m³. The pore size ranges between 0.5 and 5 mm, expediently between 0.5 and 3 mm. The weight per unit volume of the foam as well as the pore size both influence the damping effect due to the fact that a small pore size increases the frictional resistance to be overcome by the fluidic medium passing through the foam structure. In this way, midsoles can be manufactured that by selecting the appropriate pore size are tailored to the individual needs of the relevant customers.

The fluidic media to be used may be of gas as well as liquid type. With both media types the damping effect acting on the midsoles employed in accordance with the invention is based on displacement. In this respect, the compression of gas only plays a minor role; liquids are not compressible. Basically, liquids are given preference, however. It is to be understood that blends of several fluids may also be used; liquid media and gas may also be employed jointly.

Especially qualified for use as liquid media are water, oil or alcohol, or mixtures/blends of several liquids, for example of water and polyols. As oil both vegetable and mineral oil types may be used but also synthetic oil such as silicone oil. Suitable polyvalent alcohols are, for example, glycols, also oligomeric glycols, and also glycerin. If water is used, its viscosity can be increased by adding a thickening agent. This also applies to other types of liquid. The damping effect can also be controlled through the viscosity of the liquid to be displaced/shifted within the cellular structure. It is to be noted that the inventive midsole may as well be filled partly with a gaseous and partly with a liquid medium. Gaseous media in this case are primarily air, nitrogen, CO2 and also noble gases.

For the purpose of filling/refilling, the midsole is provided with a valve located at the side.

In the inventive footwear having a midsole of cellular structure said midsole is preferably arranged sandwiched between the outsole and the insole so that it is entirely enclosed. In this manner the midsole is not only protected against damage but may also be easily manufactured since there is no need to attach it to the other soles by sewing. It shall be understood that the outsole, insole, and midsole may be attached to each other by bonding/glueing or by some other process.

The inventive footwear may also be provided with additional cushioning elements that may, for example, be arranged in recesses or hollows arranged in the insole, especially in the heel and/or ball area. For this purpose, Velcro® fastening elements may be arranged in said recesses by means of which said cushioning elements are held in place. This type of touch fastening offers advantages over glueing in that the cushioning elements can be replaced as desired or necessary also with a view to lessening or improving the cushioning effect.

Naturally, the footwear proposed by the present invention may otherwise be of normal design, i.e. can be provided with any decorative elements customarily used in the footwear industry.

The sole of the inventive footwear may be of customary shape/design, that is, may be provided with a raised heel base or without raised base. The sole may be elastic and flexible or designed so as to be harder/stiffer; it may also be of convex shape which enables the foot to roll over easier.

The footwear proposed by the invention ensures that the initial contact of the heel during walking causes the medium contained in the midsole to be displaced towards the front part and into the ball area. This will bring about the damping effect the moment the heel contacts the sole. During roll-over the medium is displaced and returned into the heel area of the midsole which results in the original conditions to be restored, with a damping/cushioning effect contributing to the relief of the forefoot upon toe contact. Said reflux of the displaced medium takes place more slowly than the lifting speed of the heel which precludes additional loads from being exerted on the ankle joint.

This effect, though possibly to a slightly lesser extent, is also achieved when the midsole has been filled with gas because the compression of the gaseous medium is counteracted by the elastic material of the midsole. The energy is absorbed within the midsole also due to the time the medium needs to be displaced.

During running, the fluidic medium first distributes from the heel area towards the ball area of the foot skeleton on which the load subsequently acts. This enables the load to be absorbed over the entire foot, from the heel up to the ball and in the toe area. Even the great toe and the metatarsophalangeal joint of the great toe will absorb part of the load when lifting off. Therefore, the joint apparatus of the runner will thus have to absorb less and not additional loads.

Further elucidation of the invention is provided through the enclosed figures of preferred embodiments where

FIG. 1 is a top view of a sandal proposed by the invention;

FIG. 2 shows the sandal illustrated in FIG. 1 viewed from the toe side, and

FIG. 3 is a side view of the sandal illustrated in FIG. 1 seen from the inside of the foot.

The sandal 1 shown in FIG. 1 has a midsole 2 into which a valve element has been integrated. Valve element 7 enables the fluidic medium in the midsole to be filled in initially, and, as the case may be, replenish or replace it afterwards. Preferably, valve 7 is of self-closing design but may also be closed by means of a plug, or may be closed off by welding. In the latter case, the sole cannot be refilled.

The sandal itself is provided with a strap construct 6 to secure the sandal to the foot of the wearer, said construct being anchored in the sole construct 2/3 via two rear fasteners 4 and one front-side fastener 5. Fasteners 4 and 5 extend through the midsole 2 and project into outsole 3, and they are anchored in outsole 3 by dish-shaped enlargements 8 (see FIGS. 2/3. It is easily seen that fasteners 4 and 5 extend through ducts arranged in and passing through midsole 2 which enables a sheathing to be achieved that is impervious to the fluidic medium present in midsole 2.

Fastener 5 with strip 9 is arranged in the front region of the sandal in such a manner that wearers of the sandal can hold strip 9 between their great and second toes. Strip 9 is bonded or sewed to the strap construct 6 and extends together with fastener 5 through the sole construct 2/3 terminating in the dish-shaped enlargement 8 of fastener 5 in the outsole 3.

It shall be understood that the dish-shaped enlargements 8 of fasteners 4 and 5 are countersunk into the sole at the underside (outsole 3) and upper side (midsole 2 or, as the case may be, an insole) so that they do not project.

FIG. 2 shows the sandal as per FIG. 1 viewed from the toe side. Midsole 2 and outsole 3 which is arranged underneath the midsole can be seen with the outsole embracing the midsole 2 laterally. In this manner, the outsole 3 extending around the sides provides protection of the midsole 2. Valve 7 arranged in midsole 2 has also be shown.

Strap construct 6 is anchored in outsole 3 via fasteners 4 arranged in the heel area, with dish-shaped enlargements 8 being located in the outsole area, said enlargements being sunk into outsole 3. Fasteners 4 and 5 are secured in the outsole 3 via these dish-shaped enlargements 8. The dish-shaped elements 8 may be attached to the outsole by bonding or welding.

It can be seen that fasteners 4 and 5, with the latter merging into strip 9, extend in ducts arranged in the midsole, wherein the duct sheathings provide protection against the filling of the midsole. Strip 9 is attached to the strap construct by bonding or sewing.

FIG. 3 is a side view of the sandal shown in FIGS. 1/2 seen from the inside of the foot. The illustration shows strap construct 6 with strip 9, the midsole with valve 7 as well as the fasteners 4 and 5 with the dish-shaped retaining elements 8. It can also be seen that in the area of the toes and heel the outsole 3 has been raised to laterally embrace the midsole, with the outsole thus providing protection of midsole 2 not only in the front but also in the rear area.

It shall furthermore be understood that the sandal shown is only an embodiment of the invention. The footwear proposed by the invention may as well be designed as a conventional shoe or as a slipper with open or closed heel portion. As a rule, the outsole is stiffer than the midsole. In the heel area the outsole may transition into a raised heel base whereas in the central area the sole may also be provided with a camber or concavity which increases the efficiency of the rollover mechanism. It is essential, however, that the midsole 2 is appropriately designed so that during roll-over of the foot the fluidic medium is caused to be displaced within the midsole as a result of the running/walking movement. 

1. Footwear comprising a multi-layer structure of the sole, with said sole being composed of at least one outsole (3) and one midsole (2), wherein the midsole (2) is made of an elastic material having an open-cell structure provided with a gas- and liquid-tight outer skin, wherein said cell structure is filled at least partially with a fluidic medium
 2. Footwear according to claim 1, wherein the elastic material has a spongelike structure.
 3. Footwear according to claim 1, wherein the elastic material is a foamed plastic.
 4. Footwear according to claim 3, wherein the foamed plastic consists of an open-pore foam.
 5. Footwear according to claim 3, wherein the foamed plastic has a volumetric weight ranging between around 40 and around 100 kg/m³.
 6. Footwear according to claim 3, wherein the size of the pores is in the range of between around 0.5 and around 3 mm.
 7. Footwear according to claim 1, wherein the fluidic medium is a liquid medium.
 8. Footwear according to claim 7, wherein the liquid medium is one or more of water, polyol and a mixture thereof.
 9. Footgear according to claim 8, wherein the liquid medium is water containing a thickening agent for the purpose of increasing the viscosity.
 10. Footgear according to claim 5, wherein aside from the liquid medium the midsole (2) also contains air.
 11. Footgear according to claim 1, further comprising a valve (7) arranged in the midsole (2).
 12. Footgear according to claim 1, wherein the midsole (2) is sandwiched between the outsole (3) and an insole, with the outsole (3) being designed so as to be harder than the insole.
 13. Footgear according to claim 1, by further comprising an insole provided with recesses intended for the integration of cushioning elements.
 14. Footgear according to claim 13, wherein the recesses are located in at least one of the heel and ball area.
 15. Footgear according to claim 10, wherein the recesses are provided with Velcro® elements.
 16. Footgear according to claim 1, wherein said footgear further comprises sandals.
 17. Footgear according to claim 1, wherein said footgear further comprises flip-flops. 